All boats manufactured or imported on or after November 1, 1972 must bear a HIN.
HIN Formats Before August 1, 1984
The boat manufacturer must display two identical hull identification numbers, no less than one-fourth of an inch high, on each boat hull. The primary HIN must be permanently affixed (so that it can be seen from outside the boat) to the starboard side of the transom within two inches of the top of the transom, gunwale, or hull/deck joint, whichever is lowest. On boats without transoms or on boats on which it would be impractical to the transom, the HIN must be affixed to the starboard outboard side of the hull, aft within one foot of the stern and within two inches of the top of hull side, gunwale, or hull/deck joint, whichever is lowest. The starboard outboard side of the hull aft is the preferred HIN location for many manufacturers. On catamarans and pontoon boats the HIN must be affixed on the aft crossbeam within one foot of the starboard hull attachment.
It looks like GB chose to also place one on a plate near the lower helm station as well.